1. Field of the Invention
This invention relates to carrier devices for holding electronic components during testing and processing, and more particularly to a carrier for an integrated circuit chip which has surface electrical contact pads but no leads.
2. Description of the Prior Art
Various carrier devices have been developed to hold a semiconductor chip during testing and manufacturing operations. The available carriers are generally designed for standard chips with an array of lead pins extending out from the opposite sides of the chip. These carriers typically hold the chip in place by means of lips or rails which extend over the top of the chip along opposed edges. With this type of arrangement the upper surface of the chip is partially covered, but electrical connections with the chip can be made while the chip is still in the carrier by contacting its leads. The carriers are generally designed with industry standard outer geometries to facilitate automatic handling in bowl feeds, etc.
The above type of carrier can also be employed to hold a leadless chip, which is a chip in which electrical connections are made by contacting conductive pads on the upper surface of the chip directly, without the use of leads. Unfortunately, present carriers are not specifically designed for leadless chips, and the type of testing that can be performed while the chip is still in the carrier is limited because the lips or rails typically block at least part of the surfaces of some of the contact pads. While enough of the pad area is usually exposed for probing by a single pin, difficulties are encountered when it is desired to probe a pad with two pins simultaneously. Such double pin contact is employed in a testing technique commonly referred to as Kelvin probing. With this technique probing by the second pin is used either for redundant testing, or as a safety device in which the second probe is used to prevent the imposition of an accidental overload on the chip from the first probe. With conventional chip carriers Kelvin probing is not feasible because of the partial blockage of at least some of the contact pads.
U.S. Pat. No. 3,417,865 to Suverkropp et al. is illustrative of a prior type of chip carrier. It discloses a carrier which is designed for a chip with leads, the leads being received in a series of grooves formed between longitudinal ribs on the upper surface of the carrier. Some of the ribs are extended so that they overlie an open area reserved for the chip and hold the chip in place, the chip being inserted by placing it over these ribs and forcing it down until the ribs snap in place overhead. Another prior art carrier is shown in U.S. Pat. No. 3,652,974 to Tems. In this patent flexible side walls surrounding the chip area flex outward to permit the insertion of a chip, and then flex back against the chip to hold it in place. Retainer projections extend from the side walls over the chip to hold it down. In U.S. Pat. No. 3,604,557 to Cedrone the chip is placed in a recess which can be widened by squeezing the carrier to permit insertion of the chip, with the side walls gripping the chip when the carrier is released. A series of ribs are provided along opposite sides of the recess to accommodate the leads, and also extend over the chip to hold it in place. In all of these patents it is possible for at least some of the contact pads of a leadless chip to be blocked sufficiently to prevent Kelvin probing. In addition, the chips are loaded and unloaded from the top by applying pressure directly onto their major plane, and accordingly are stressed to a greater degree than if they could be loaded from the side without having to press down into the plane of the chips.
Other testing devices are available, commonly referred to as "naked handlers", which present individual chips to a contacting device without the use of a carrier. Leadless chips are so small, however, that Kelvin probing generally cannot be accomplished with these devices unless the chip is held in place. Holding devices are available, but they extend over the upper surface of the chip so as to partially block at least some of the contact pads, resulting in the same problem of access to the pads of a leadless chip as in conventional carrier devices.
One type of chip holder that does not cover up part of the contact pads of a leadless chip is a test socket which is normally committed to a printed circuit board for burn-in testing. This type of socket, however, is not mobile and does not lend itself to automatic loading of the chip into various testing and manufacturing machines, and is top loaded.